GENEEA AKD GROTJPS OF THE ECHINOIDEA. 215 



at the peristome is small, and tlie next is larger and single, the 

 arrangement being meridosternous ; the plates are slightly pro- 

 duced backwards so as to form a slight beak-like structure which 

 is placed below the periproct. 



The peristome is far iu front and is pentagonal ; it has irre- 

 gularly concentric rows of plates on its membrane. Periproct 

 nearly circular in outline, largely plated, and placed above the 

 keel-like margin of the posterior part of the test. A narrow 

 marginal fasciole exists, and it dips below the edge anteriorly. 



The ornamentation of the test is small and simple, the 

 two or three small primaries, which are on each ambulacral and 

 interradial plate abactinally, are irregularly placed, and there 

 are some granules with them ; there are larger tubercles which 

 are rather crowded along the sternal keel, and also on the pos- 

 terior part of the abactinal surface. In these places the spines 

 are largest and paddle-shaped and striated ; similar spines are 

 also around the periproct. The tubercles elsewhere carry slender 

 hair-like or blunt-ended and notched spines. Colour of the test 

 pale green. 



Becent. North of Bermuda, 2650 fathoms. 



Genera incertae sedis : Enichaster. 

 Sienonia. 



Grenus Ekichastee, De Loriol, 1882, Descr. des Echinides des 

 Env. de Camerino, Mem. Soc. PJiys. et Hist. Nat. de Oenhve, 

 t. xxviii. No. 3, p. 30. 



The test is much longer than broad, oval-elliptical in marginal 

 outline, without notches ; slightly convex dorsally and actinally, 

 moderate in size and greatly depressed. 



The apical system is excentric in front, compact, and has 

 four close, perforated basal plates. Madreporite surrounded by 

 the basals, and very small. 



Ambulacra flush with the test, showing no tendency to closing ; 

 the anterior has no groove, and is composed of very minute pores 

 which are wide apart. The antero-lateral ambulacra are almost 

 transverse, and the poriferous zones are equal ; the pores are in 

 simple pairs, round, and not united by a groove. The posterior 

 ambulacra are the longest and closest. 



The excentinc-in-front peristome was probably pentagonal. 

 The periproct opens quite at the summit of the posterior inter- 



